Before you buy it, ask him to hook it up to water and electric, then turn on the hot water heater, the ac, then test the furnace. Flush the commode, turn on faucets and look under the counters, under the rig, and anywhere else for leaks. If you ever plan on dry camping you should also add water to the freshwater tank and turn on the 12 volt water pump to see if it works.
Tires are a big expense, so look at the DOT number on the tires and the last 4 digits should indicate the yr of the tires. Example (3210) would indicate the tires were made in the 32nd week of 2010. If they are 4 or 5 yrs old they will need to be replaced before taking any trips. $500 or more there for decent tires.
The weight ditribution hitch should come with a sway control bar. I see them all day long on craigslist from $125 to $250.
This may sound like a lot to ask of your friend, but it's not a trust your friend issue, it's to learn how to use all the features and that would be how to present it. Of course in the process you can find out what really works or does'nt.
Also, if the wheel bearings have not been packed in the last few years, you need to know.
Last but not least, climb on the roof and see if there are any soft spots or caulking that needs to be replaced.Look closely inside around windows and walls, and in closets for any stains indicating a leak. Make sure there are no soft spots in the floor.
If all this passes you are getting a steal of a deal. If you find any issues and dont know how to fix it yourself you will be terribly dissapointed with the cost of repairs at the dealerships. Usually $100 bucks per hr.
Nothing beats an enjoyable campout with a rig you can trust, and there's nothing more miserable than fighting problem after problem.
Best of Luck to Ya!